The upgraded A428 will help provide “great economic benefits” for communities in Huntingdonshire, the district council has said.
Highways England announced on Monday (February 18) that a preferred route for the new road, which will run between Black Cat and Caxton Gibbet, had been selected - known as option C.
Highways England says tens of thousands of drivers who use the A1, A421 and the A428 could benefit from the new 10-mile dual carriageway that will stretch from the Black Cat junction to the Caxton Gibbet roundabout.
The existing A428 will become a local road which will serve the communities between St Neots and Caxton Gibbet.
Options for the new road scheme were put to the public in 2017, and the route announced last week combined what Highways England described as a "mix of benefits" and the "most popular options at consultation".
The upgrade will also includes improvements to the A428/B1040 Eltisley junction, and there will be improved routes for cyclists, walkers and horse riders.
Councillor Ryan Fuller, executive councillor for housing, planning and economic development at Huntingdonshire District Council, said: "The council is absolutely delighted that long-awaited improvements to the A428 have finally been confirmed. This new route, which was broadly the council's preference amongst the options, will begin to redress existing deficiencies in the road network.
"Critically, it will begin to reduce constraints to both local and wider cross country journeys, and give much greater certainty about the ability to move around within our District efficiently and effectively."
Cllr Fuller added: "Improved certainty in journey times will aid business confidence for future investment in employment opportunities, and help existing and future residents make more informed choices around the ability to live and work successfully across Huntingdonshire.
"Mitigation can be provided in terms of matters such as noise and air quality in order to protect St Neots now, and as part of planned growth which is a key consideration for this council.
"Coming alongside the current east west rail consultation, these are all exciting announcements that increasingly demonstrate that Huntingdonshire is a strong and sustainable place for growth, providing great future economic benefits for our communities."
It is hoped work on the upgrade will begin by April 2022.